Doub"let (?), n. [In sense 3, OF. doublet; in sense 4, F. doublet, dim. of double double. See Double, a.] 1. Two of the same kind; a pair; a couple.

2. (Print.) A word or words unintentionally doubled or set up a second time.

3. A close-fitting garment for men, covering the body from the neck to the waist or a little below. It was worn in Western Europe from the 15th to the 17th century.

4. (Lapidary Work) A counterfeit gem, composed of two pieces of crystal, with a color them, and thus giving the appearance of a naturally colored gem. Also, a piece of paste or glass covered by a veneer of real stone.

5. (Opt.) An arrangement of two lenses for a microscope, designed to correct spherical aberration and chromatic dispersion, thus rendering the image of an object more clear and distinct. W. H. Wollaston.

6. pl. (See No. 1.) Two dice, each of which, when thrown, has the same number of spots on the face lying uppermost; as, to throw doublets.

7. pl. [Cf. Pr. doblier, dobler draughtboard.] A game somewhat like backgammon. Halliwell.

8. One of two or more words in the same language derived by different courses from the same original from; as, crypt and grot are doublets; also, guard and ward; yard and garden; abridge and abbreviate, etc.

• a man's close-fitting jacket, with or without sleeves. Men in Europe wore doublets from the 1400's to the 1600's.
  
• a pair of two similar or equal things; couple.
  
• one of a pair.
  
• one of two or more different words in a language derived from the same original source but coming by different routes. Examples: (1) aptitude and attitude. Aptitude came into English as a direct borrowing from Late Latin aptitudo, aptitudinis. However this Latin word was taken into Italian in the form attitudine, which was later further changed to attitude in French, from which it came into English. (2) fragile and frail. Fragile came into English as a direct borrowing from the Latin fragilis. However, the word fragilis changed to frele (or fraile) in French, from which it came into English in the form frail.
  
• an imitation gem made of two pieces of glass or crystal with a layer of color between them.
  
• Printing, U.S. a word or phrase set a second time by mistake.